 public class xiti3_7_1 {
   public static void main(String[] args) {
     int i=1,n=21;
     double sum = 0, item =1;
     do{
       sum=sum+item;
       i=i+1;
       item=item*(1.0/i);
     }while(i<=n);
     System.out.println(sum);
   }
 }
